This invention relates generally to radiation apparatuses and methods, and in particular to multileaf collimators and methods of adjusting radiation beams useful in radiotherapy and other industries.
Multileaf collimators (MLCs) are widely used in radiotherapy machines to support various treatments including intensity-modulated radiation therapy (IMRT) and arc therapy, etc. Conventional multileaf collimators include a single level of a plurality of beam blocking leaves arranged in two opposing banks or arrays. Each leaf in a bank is longitudinally movable relative to a leaf in the opposing bank. In operation each of the individual leaves is positioned to block a portion of a radiation beam passing through the volume occupied by the leaf. The combined positioning of all leaves defines one or many apertures through which the unblocked radiation beam passes, and the aperture(s) define(s) the shape of the radiation beam directed to a treatment field at an isocenter.
To mitigate radiation leakage in single level MLCs, various leaf designs are developed including “tongue in groove” designs in which steps, waves or similar geometries are provided on the leaf sides so that leaf materials mutually overlap between leaves as viewed from a radiation source. While a tongue in groove design may reduce leakage between leaf sides, it unfortunately leads to undesirable underdose effects when MLC treatment fields are combined. Some conventional MLCs are used in combination with one or two pairs of collimation jaws to reduce leakage between abutted leaf ends. One issue associated with the combination of a MLC with collimation jaws is the increased bulk of a radiation system and the resulting reduced clearance between the patient and moving equipment.
It is desirable to provide MLCs that can shape beams with high resolution so that the shaped beam conforms to a target volume as close as possible. In general a MLC would provide for higher beam shaping resolution if the beam blocking leaves could be thinner. However, reducing the width of leaves to improve MLC resolution has limitations and imposes challenges to MLC construction and operation. For MLCs using screw leaf drive systems for example, long slender drive screws may be susceptible to column buckling in a way that scales dramatically worse with smaller screw diameters. Motors with a smaller diameter may also be required.